Photochemical- and pH-switching Properties of a New Photoelastic Ligand Based Upon Azobenzene. Basicity and Anion Binding |
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Authors: | Andrea Bencini Claudia Giorgi Emiliano Romagnoli Carlos Lodeiro André Saint-Maurice |
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Affiliation: | 1. Department of Chemistry , University of Florence , Via Maragliano 75/77, 50144, Florence, Italy;2. Departamento de Química, Centro de Química-Fina e Biotecnologia, Faculdade de Ciěncias e Tecnologia , Universidade Nova de Lisboa , Quinta da Torre 2825, Monte de Caparica, Portugal |
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Abstract: | Abstract The synthesis of a new cylindrical macrotricyclic ligand (L) based upon two 1,4,7,13-tetramethyl-1,4,7,10,13,16-hexaazacyclooctadecane rings connected via two azobenzene pillars is described. The ligands displays photoelastic properties: light absorption at 366 nm produces trans→cis isomerization of the azobenzene moieties with formation of trans-cis (L E-Z ) and cis-cis (L Z-Z ) isomers. Recovery of the thermodynamically more stable trans-trans (L E-E ) isomer can be obtained by thermal back-isomerization or visible light (430 nm) absorption. The isomeric composition of L solution depends upon pH: for pH < 5.5 the L E-E form is the unique species in solution, while increasing amounts of Z species are formed at increasing pH. The protonation constants of L E-E have been determined in 0.1 mol dm?3 Me4NNO3 solution at 298.1 ± 0.1 K. The protonated species of L form stable inclusion complexes with anionic species such as [Co(CN)6]3?. |
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Keywords: | Photoelastic ligands Chemical switches Macrocycles Anion coordination |
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